-- simple root-finding
f x = x^2 - 100
rootf f a b
  | abs(a-b) < epsilon = c
  | (f a)*(f c) < 0    = rootf f a c
  | (f a)*(f c) > 0    = rootf f c b
  | f a == 0            = a
  | f b == 0            = b
  | f c == 0            = c
  where epsilon = 0.00001
        c = (a+b)/2